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From Eric Owhadi <eric.owh...@esgyn.com>
Subject investigating MDAM
Date Thu, 25 Feb 2016 22:39:38 GMT
Hi Trafodioneers,

Can someone explain or point me to the source file that is handling mdam
probing?

I think I found anomaly on cache size and small scanner when using MDAM,
but would like to make sure, therefore would like to understand how  the
probing works in MDAM…

Thanks in advance for the help,

Eric



FYI, my test shows 4010  IO to go over 1000 MDAM ranges:

So 4 IO per range: I am assuming

-Open scanner?

-Fetch?

-Close scanner?

-Then another one for probing? I would assume it is a get, is it?



So the problem I am seeing is that both cachesize and small scanner logic
are not taking into account the split of scan into smaller chunk with MDAM.
So I am searching if compiler knows in advance how many chunk MDAM will end
up using? Is there a tdb value that is carrying this info?

The consequence of this is that we are using higher cache size than needed,
and we are not benefiting from small scanner faster speed/lower IO with
MDAM.





See below:



create table t132helper (a int not null, primary key(a));

insert into t132helper values(1);

create table t132 (k1 int not null, k2 int not null, a int not null, b int
not null,

     c
char(1000),
primary key (k1,k2)) ATTRIBUTES ALIGNED FORMAT ;

upsert using load

into t132

  select  x1000*1000+ x10000*10000 + x100000*100000,

          x1+x10*10+x100*100,

          x1+x10*10+x100*100+ x1000*1000+ x10000*10000 + x100000*100000,

          x1+x10*10+x100*100+ x1000*1000+ x10000*10000 + x100000*100000,

          'yo bro'



  from t132helper

transpose 0,1,2,3,4,5,6,7,8,9 as x1

transpose 0,1,2,3,4,5,6,7,8,9 as x10

transpose 0,1,2,3,4,5,6,7,8,9 as x100

transpose 0,1,2,3,4,5,6,7,8,9 as x1000

transpose 0,1,2,3,4,5,6,7,8,9 as x10000

transpose 0,1,2,3,4,5,6,7,8,9 as x100000;

update statistics for table t132 on every column;



select count(*) from t132 where k2 between 10 and 21;

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